1. Field of the Invention
The present invention relates to an image scanning apparatus which scans images on an original (something to be subjected to scanning, having images or letters printed on) using an image sensor. In addition, the present invention relates to an image scanning apparatus which optically scans images on an original, a recording medium which stores image scanning programs which causes a computer to execute control over the image scanning apparatus, and a data structure for coding and transmitting the image scanning programs.
2. Description of the Related Art
Some image scanning apparatuses sense light reflected from or transmitted through an original using a line sensor or area sensor and generate image data. The line sensor is an image sensor having a one-dimensional arrangement of pixels, while the area sensor is an image sensor having a two-dimensional arrangement of pixels.
In such an image scanning apparatus, a color image is scanned by switching illumination directed upon an original between light of three colors, i.e., red light (R), green light (G), and blue light (B), or by using an image sensor including a color filter.
For example, in an image scanning apparatus including a line sensor as an image sensor, a color image is scanned on a line basis as shown in FIGS. 8(a) and 8(b).
Note however that FIG. 8(a) shows the timings to read image data on a line basis in a line sequence method using a monochrome line sensor. In the line sequence method, the illumination is switched among light of three colors, red light (R), green light (G), and blue light (B) on a line basis. Meanwhile, FIG. 8(b) shows the timings to read image data on a line basis using a color line sensor.
Note that, in FIGS. 8(a) and 8(b) and later-described FIGS. 9(a) and 9(b), in each of the line sensors, photoelectric conversion is performed at the light receiving part of each pixel, and signal charges corresponding to light reflected from or transmitted through an original are generated. The generated signal charges are transferred to a transferring unit in response to a predetermined line sensor clock signal, and output as image data. Signal charges generated at the light receiving part of each pixel during the transition between lines to be scanned, (i.e., signal charges generated at the light receiving part of each pixel while the original or line sensor is moved) are output as invalid data not corresponding to the image data before the image data for the next line is output. Hereinafter, such an output is referred to as invalid output.
Now, FIGS. 8(a) and 8(b) will be described.
In FIG. 8(a), during the invalid output period, signal charges corresponding to the red light (R) are generated. While the signal charges corresponding to the red light (R) are being output as image data (in other words during the R output period), signal charges corresponding to the green light (G) are generated. While the signal charges corresponding to the green light (G) are being output as image data (in other words during the G output period), signal charges corresponding to the blue light (B) are generated. The signal charges corresponding to the blue light (B) are output as image data (which corresponds to the B output) before signal charges for the next line corresponding to the red light (R) are generated.
Meanwhile, in FIG. 8(b), during the invalid output period, signal charges for white light are generated. Note that the signal charges generated at the time are signal charges corresponding to the red light (R), the green light (G) and the blue light (B) filtered through the color filter. These signal charges are output as image data (which corresponds to the R, G and B outputs) before signal charges for the next line are generated.
In an image scanning apparatus which scans images on a film original (hereinafter referred to as the “film scanner”), it is known that defects such as dust, dirt, marks and fingerprints present on the film original appear as spots on the scanned images. These spots could degrade the picture quality. The spot appears as a black spot in a positive film, while it appears as a white spot in a negative film. Herein, the film original is for example a negative film, a reversal film or an elongated film.
In recent years, techniques of detecting defects such as dust, dirt, marks and fingerprints on the film original have been developed to restrain from degradation in picture quality. According to the techniques, an infrared image by infrared light (Ir) is scanned in addition to a color image. Such a technique takes advantage of the characteristic that infrared light (Ir) is transmitted through a film original virtually intact except for parts shut out by the defects such as dust, dirt, marks, and fingerprints. Methods of processing images to compensate for the influence of the defects thus detected have been also implemented.
These techniques may be applied to a film scanner having a monochrome line sensor or a color line sensor, so that color and infrared images can be scanned on a line basis at timings as shown in FIGS. 9(a) and 9(b).
More specifically, in FIG. 9(a), similarly to FIG. 8(a), the invalid output, the R output, and the G output are provided, and then during the following B output period, signal charges corresponding to the infrared light (Ir) are generated. The signal charges corresponding to the infrared light (Ir) are output as image data before signal charges for the next line corresponding to the red light (R) are generated. (This output corresponds to the Ir output.)
In FIG. 9(b), similarly to FIG. 8(b), the invalid output is provided, and then during the R, G and B output period, signal charges corresponding to the infrared light (Ir) are generated. The signal charges corresponding to the infrared light (Ir) are output as image data before signal charges for the next line are generated. (This output corresponds to the Ir output.)
Meanwhile, a normal monochrome line sensor or a normal color line sensor is not adapted to infrared radiation, and therefore signal charges by the infrared light (Ir) are generated at other than at the light receiving part (at the transferring unit for example) which should be shut out against illumination.
More specifically, in FIG. 9(a), during the period in which infrared light (Ir) is irradiated and signal charges corresponding to the infrared light (Ir) are generated, image data for the blue light (B) output through the transferring unit could include additional signal charges by the infrared light (Ir). In FIG. 9(b), during the period in which infrared light (Ir) is irradiated and signal charges corresponding to the infrared light (Ir) are generated, the image data of each color output through the transferring unit could also include additional signal charges by the infrared light (Ir).
In a line sensor in general, the brightness is represented by the amplitude difference between a pre-charged portion (reference) and a data portion. More specifically, the image is darker for smaller amplitude difference and brighter for greater amplitude difference. As shown in FIG. 10, when the original amplitude V1 is added signal charges by the infrared light (Ir) and causes the signal fluctuates, the amplitude is changed to V2.
Therefore, in a film scanner in which each line is scanned in the timings as shown in FIGS. 9(a) and 9(b), the generation of image data by the infrared light (Ir) causes the picture quality in a color image to be degraded.
Such degradation in the picture quality could also be encountered in a film scanner to scan images on a film original in a page sequence method using a monochrome line sensor or using an existing area sensor, or an image scanning apparatus to scan images on an original based on light reflected from the original.
Note that in the page sequence method, all the lines within a scanning area are sequentially scanned using illumination of a single color, and the process is repeated using illumination of all the other colors.
A conventional line sensor is composed as shown in FIG. 11.
In FIG. 11 a line sensor 100 is composed of a sensor 101 wherein a plurality of photoelectric sensors are arranged in a row corresponding to a light receiving part, a charge transfer register 102 comprising a CCD formed in correspondence to each photoelectric sensor of the sensor 101, an read out gate (ROG) 103 disposed between the sensor 101 and the charge transfer register 102, and a charge-to-voltage converter 104 disposed on the output end of the charge transfer register 102.
A signal charge that corresponds to the reflection light and the transmission light of the original is generated at each photoelectric sensor of the sensor 101 between the time when the illumination is irradiating and the read out gate 103 reads out the signal charge generated in this manner to the charge transfer register 102 in correspondence to a clock pulse φROG. The charge transfer register 102 sequentially transfers the signal charge read out in this manner to the charge-to-voltage converter 104 and the charge-to-voltage converter 104 converts the signal charge to a voltage and outputs the voltage as image data.
In this type of line sensor 100, the quantity of light irradiated onto the photoelectric sensor can be controlled by means of adjusting the time the illumination lights and a color image can also be scanned by means of switching the illumination between light of three colors, red light (R), green light (G), and blue light (B), or by providing a color filter.
As shown in FIG. 12, a color image is scanned in a conventional image scanning apparatus provided with this line sensor 100.
FIG. 12(a) shows the timings to scan one line of a color image using the line sequence method in like manner to FIG. 8(a) using the line sensor 100 as a monochrome line sensor. FIG. 12(b) shows the timing to scan an entire color image using the line sensor 10 as a color line sensor when a color filter is provided.
When red light (R) is illuminated while scanning a color image as shown in FIG. 12(a), a signal charge is generated that corresponds to the red light (R) at each photoelectric sensor of the sensor 101. The signal charge that corresponds to the red light (R) generated in this manner is read out to the charge transfer register 102 while clock pulse φROG is at a high level. The signal charge is then sequentially transferred to the charge-to-voltage converter 104 by the charge transfer register 102 while clock pulse φROG is at a low level, converted to a voltage by the charge-to-voltage converter 104 and finally output as valid image data (R output).
Furthermore, while this type of R output is being performed, green light (G) is illuminated and a signal charge that corresponds to the green light (G) is generated. Then, in like manner, blue light (B) is illuminated and a signal charge that corresponds to the blue light (B) is generated while G output is being performed.
In addition, while B output is being performed, the output before illumination is turned off and R output is performed is handled as invalid data.
In contrast, when white light is illuminated while scanning a color image as shown in FIG. 12(b), signal charges are generated which correspond to red light (R), green light (G), and blue light (B) filtered through the color filter at each photoelectric sensor of the sensor 101. These types of signal charges are read out to the charge transfer register 102 while clock pulse φROG is at a high level and are sequentially transferred to the charge-to-voltage converter 104 by the charge transfer register 102 while clock pulse φROG is at a low level, converted to voltages by the charge-to-voltage converter 104 and finally output as valid image data (R, G, B outputs).
While these types of R, G, B outputs are being performed, the output before white light is illuminated, the signal charge in the next line is generated and the R, G, B output of the top line is performed is handled as invalid data.
In other words, if clock pulse φROG changes from a high level to a low level while scanning a color image as shown in FIG. 12, the transfer of the signal charge by the charge transfer register 102 and the voltage conversion of the signal charge by the charge-to-voltage converter 104 will begin accompanied by the illumination irradiating and signal charges being generated at each photoelectric sensor of the sensor 101.
The charge-to-voltage converter 104 is provided in the line sensor 100 in order to convert signal charges supplied from the charge transfer register 102 to a voltage. Because of these characteristics, there is only a slight property that generates signal charges in response to light.
Consequently, as shown in FIG. 12, besides the actual function signal charges are generated in the charge-to-voltage converter 104 during the period in which R output, G output or R, G, B outputs (excluding the final line) is performed as well as while the illumination is irradiating. Because, together with signal charges supplied from the charge transfer register 102, signal charges generated in this manner are converted to a voltage, excess voltage is accumulated equivalent to signal charges generated by the charge-to-voltage converter 104 for the voltage equivalent to signal charges supplied from the charge transfer register 102.
In other words, a problem occurred wherein incorrect image data different from the original images is generated due to the effect of the signal charges generated by the charge-to-voltage converter 104 in the line sensor 100 utilized in image scanning apparatuses which scan color images at the timings shown in FIG. 12. The worst case resulted in blooming, smearing or similar phenomenon occurring.
To decrease the occurrence of noise in recent years, line sensors have been put into practical use having charge-to-voltage converters that have a high conversion efficiency when converting signal charges to voltages. In this type of line sensor, however, the above-mentioned phenomenon occurs quite often.
In addition, the above-mentioned problems are not limited to cases when scanning color images but also cases when valid signal charges as image data generated at each photoelectric sensor of the sensor 101 are voltage-converted in parallel with the illumination being turned on. The problems can also occur in image scanning apparatuses having area sensors (for example, occurs when switching the color of the illumination and scanning color images of an original). Even further, the same type of problem occurs when generating signal charges not only at the charge-to-voltage converter 104 but also at the charge transfer register 102 or the read out gate 103.
A method wherein the charge-to-voltage converter 104 is physically shielded such that illumination is not allowed to strike the charge-to-voltage converter 104 has been considered as a means to solve the aforementioned problems. However, since there is a short distance between the charge-to-voltage converter 104 and the photoelectric sensor of the sensor 101, the method to shield the charge-to-voltage converter 104 also causes the photoelectric sensor at the top of the sensor 101 to be shielded as well. Consequently, this method is not advised.